1. Field of the Invention
The present invention relates to a hard disk drive (HDD), and more particularly to a technique for detecting a stiction error which may be caused by a friction force between a head and a disk in the hard disk drive.
2. Description of the Related Art
With the high storage capacity and the high access speed, a hard disk drive which reads and writes data from and onto a rotating magnetic disk is widely used as an auxiliary memory of a computer system. Such a hard disk drive writes information on tracks arranged along concentric circles on the rotating magnetic disk. A magnetic head accesses the tracks to read and write data from and onto the magnetic disk. In such a hard disk drive, upon a power-up, a controller drives a spindle motor for rotating the magnetic disk in order to initialize the system. In the meantime, when the spindle motor rotates at 1000 rpm, the magnetic head rises from the surface of the magnetic disk. When the spindle motor rotates at a steady-state rotation speed, the system drives a voice coil motor (VCM) for moving the magnetic head. However, when the spindle motor is driven upon the power-up, the magnetic head rubs against the magnetic disk, disturbing a rotation of the spindle motor. Such a phenomenon is called stiction error. A spindle motor shaking technique has been proposed to get rid of the stiction error.
In a hard disk drive, a plurality of disks are rotated by a spindle motor and a plurality of magnetic heads are respectively positioned at corresponding surfaces of the disks. The magnetic heads are mounted on corresponding support arms each extending toward the disks from an assembly associated with a rotary voice coil actuator. A microcontroller generates control commands for the system in response to read and write commands received from a host computer. A voice coil motor driver generates a driving current for driving an actuator in response to a position control signal generated by the microcontroller for controlling the position of the heads. The driving current is applied to a voice coil motor of the actuator so as to move the heads on the disks according to a direction and level of the driving current received from the voice coil motor driver. A spindle motor driver drives the spindle motor according to a rotational control signal generated by the microcontroller for controlling the rotation of the disks.
An earlier spindle motor driver includes a start-up oscillator and a restart oscillator. The start-up oscillator generates a spindle motor rotation control frequency in accordance with a level of a spindle motor driving control voltage to control the rotation of the spindle motor. The start-up oscillator pulls the spindle motor driving control voltage down to 0 upon detecting a back EMF (electromotive force) signal generated by the spindle motor. The restart oscillator generates a restart control signal for periodically restarting a rotation of the spindle motor in case that the spindle motor does not rotate at a steady-state rotation speed within a predetermined time after the spindle motor has been started by the start-up oscillator. The restart control signal controls a level of the spindle motor driving control voltage applied to the start-up oscillator.
Upon the power-up of the hard disk drive, the spindle motor commonly undergoes three operating intervals. The first operating interval is a spindle motor shaking interval at which the spindle motor is shaken and the second operating interval is a spindle motor start interval at which the spindle motor starts rotating and the third operating interval is a running interval at which the spindle motor accelerates and maintains the steady-state rotation speed. In the first operating interval, when the spindle motor driving control voltage is higher than 0 and lower than the predetermined value, the start-up oscillator generates a spindle motor rotational control frequency of 176 Hz in accordance with the spindle motor driving control voltage and shakes the spindle motor in synchronism with the spindle motor rotational control frequency. In the second operating interval, when the spindle motor driving control voltage is higher than the predetermined value and lower than a second predetermined value, the start-up oscillator generates the spindle motor rotation control frequency of 8.6 Hz, and rotates the spindle motor in synchronism with the spindle motor rotation control frequency of 8.6 Hz. Then, the start-up oscillator detects the back EMF generated by the rotating spindle motor and pulls the spindle motor driving control voltage down to 0 upon detecting the back EMF signal. In the third operating interval, the start-up oscillator generates the spindle motor rotation control frequency of 176 Hz in accordance with the spindle motor driving control voltage of 0V, and rotates the spindle motor at the steady state rotation speed in synchronism with the spindle motor rotation control frequency of 176 Hz. In this manner, the spindle motor is controlled during the start-up mode when the stiction error is not generated.
However, after starting a rotation, the spindle motor may stay at the second operating interval for a long time due to the stiction error caused by the friction force between the head and the disk. In case the start-up oscillator delays proceeding to the third operating interval for one cycle of the restart control signal generated by the restart oscillator, the spindle motor driving control voltage is pulled down to a low voltage below the predetermined voltage in synchronism with the restart control signal. Then, the spindle motor again gets into the first operating interval, that is, the spindle motor shaking interval, to remove the stiction.
While a voice coil motor shaking technique is effective in removing the stiction error, it takes at least six or seven seconds to detect the stiction error when the stiction error is generated. Therefore, in case of the stiction error, it is impossible to timely shake the voice coil motor and pass a common drive delay time of fifteen seconds which may result into a system error.
The Boutaghou et al. patent, U.S. Pat. No. 5,530,602, entitled Disk Drive Micromotion Starting Apparatus And Method, discloses a starting arrangement for a rotating disk data storage device which measures the back EMF in the spindle motor windings to indicate the start of disk rotation when a stiction condition has been terminated and applies alternating current pulse burst to the actuator motor to break the stiction between the heads and the disk surfaces.
The Knappe and McAllister et al. patents, U.S. Pat. Nos. 4,970,610 and 5,397,971, entitled respectively Magnetic Disk Drive Start Procedure For Starting Reaction Torque Amplification and Bi-Polar Disk Torquing System For A Disk Drive To Free Stuck Transducers, disclose arrangements in which stiction in a magnetic disk drive is detected and pulses are applied to the spindle motor to break the stiction.
The Plutowski et al. patent, U.S. Pat. No. 5,682,334, entitled Motor Start Acceleration Profile, discloses a motor start acceleration profile arrangement which detects stiction by measuring the motor speed of the spindle motor.
The following patents each disclose features in common with the present invention but are not as pertinent as the patents discussed in detail above: U.S. Pat. No. 4,809,248 to Sengoku, entitled Memory Device Including A Rotating Disk And Means For Detecting Change In Frictional Resistance Between The Disk And A Read/Record Head, U.S. Pat. No. 5,115,664 to Hegde et al., entitled Tunable Feedback Transducer For Transient Friction Measurement, and U.S. Pat. No. 5,539,592 to Banks et al., entitled System And Method For Monitoring Friction Between Head And Disk To Predict Head Disk Interaction Failure In Direct Access Storage Devices.